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Old 03-09-2018, 15:20   #16
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Re: Are full water tanks on the hard bad for the boat?

A US liquid gallon of water weighs about 8.34 pounds or 3.78 kilograms at 62 F (17 C), making it about 16.6% lighter than the imperial gallon.
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Old 03-09-2018, 15:35   #17
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Re: Are full water tanks on the hard bad for the boat?

So how can it become
Lighter? Is that why us Americans look so big.
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Old 03-09-2018, 16:29   #18
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Re: Are full water tanks on the hard bad for the boat?

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Originally Posted by kas_1611 View Post
50 GallonsUS of diesel weighs 347.15lbs
125 GallonsUS of water weighs 1045lbs

Total weight of fluid is 1392.15lbs
2.2lbs to the kilo that is 632.8kg

I tip the scales at 74kg (163 lbs) so that is 8 1/2 me's

Weight of diesel 6.9ppg
Weight of freshwater 8.36ppg

The question was whether to empty the water tanks (1045lbs) , not fuel and water.
So that make 6 1/2 yous
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Old 03-09-2018, 16:44   #19
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Re: Are full water tanks on the hard bad for the boat?

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Originally Posted by JPA Cate View Post
He did say 175 gallons. 16 lbs per gallon (a pint's a pound, the world around), so approximately 2800 lbs, divided by 150 lbs for the people. Just approximations, but I just ran the numbers again, and my calculator says 18.66666667, so I called it 18. Figured somebody might weigh more than 150 lbs.

Ann

He was asking about the water (125 gallon) not fuel and water.
A US gallon of water weighs 8.35lb, not 16lb

There are not 16 pints in a gallon )

(A pint of pure water weights a pound and a quarter (in much of the world) )

150lb (68kg) is very light. That's way below the standard weight used for calculations such as light aircraft passengers (which are around 85kg for men and 70kg for women) I used 80kgs for the calculation.
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Old 03-09-2018, 16:51   #20
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Re: Are full water tanks on the hard bad for the boat?

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Originally Posted by Martkimwat View Post
(1800 lbs =816 kgs = 816 imp. galls)
1800 lbs = 816 kgs = 215 US gallons or 179 Imp gal
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Old 03-09-2018, 17:02   #21
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Re: Are full water tanks on the hard bad for the boat?

Good point, Stu M, the OP did not mean to include the fuel in the calculations.

There are 2 pints to a quart, and 4 quarts to a gallon, so that's where I made my repeated error. Thanks for catching it.

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Old 03-09-2018, 17:13   #22
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Re: Are full water tanks on the hard bad for the boat?

No need to get all wrapped up in the math. For these kindsa calculations, 2 decimal places tend to amount to spurious accuracy.

A gallon of fresh water weight 8 1/4 lbs close enuff. 125 x 8 = 1,000. Toss in 30 lbs to allow for the 1/4, and Bobs yer uncle. Then there's the 50 gallons aft. 1,000 dived by 5 is 200. 200 x 2 is 400. So what you hull has to carry is the equivalent of five healthy lads forward, a two healthy lads and a small dog aft.

Don't we all carry the answers to those sorts of "good enuff" calculations in our heads, so we don't have to drag out the fancy new-fangled electronic abacuses every time we need such an answer :-)?

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Old 03-09-2018, 19:53   #23
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Re: Are full water tanks on the hard bad for the boat?

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Originally Posted by TrentePieds View Post
Don't we all carry the answers to those sorts of "good enuff" calculations in our heads, so we don't have to drag out the fancy new-fangled electronic abacuses every time we need such an answer :-)?

TP
It's much easier if you do it in metric.
If the OP had told us he had a 280 litre (kg) tank forward and a 190 litre (kg) tank aft, it would be obvious that that's about 3 largish men forward and 2 aft.
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Old 03-09-2018, 19:59   #24
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Re: Are full water tanks on the hard bad for the boat?

I am pretty sure diesel is about 6.9 pounds imperial gallon.
Not that it makes a lick of difference but if my boat was to fragile to hold a bit of water in the tank on land then that is where I would want it to fail. Not slapped to pieces from the force of the ocean slamming a lot harder than a tank of water just sitting there
Just saying
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